This invention relates to amplifiers for use in communications systems and, more particularly, to amplifiers that inhibit or reduce inter-modulation interference in composite signals.
In some communications systems such as, for example, very small aperture transmission (VSAT) systems, modulated-information signals are typically transmitted with other component signals in a composite signal. In a VSAT system, the other component signals may be, for example, a clock signal and DC power.
When a long cable is needed to couple two elements in a communications system (e.g., a transmitter to a receiver, an antenna to a downlink or an uplink converter) signal losses due to noise, dielectric loss, resistivity, and interference in the cable may reduce the composite signal to an unusable level. These losses may increase as the frequency of the transmitted signals increase. More energy may be dissipated as the frequency increases. When standard low-cost off-the-shelf line amplifiers are used to adjust or compensate for these signal losses, the component signals may interfere with each other rendering the composite signal unusable. This inter-signal interference is sometimes referred to as “inter-modulation” interference.
It is therefore an object of the present invention to provide a line amplifier that inhibits or reduces inter-modulation interference.